This invention relates to filaments of crystalline plastics possessed of excellent mechanical properties because of a stretching treatment and to a method for the manufacture of such filaments.
In producing filaments by the melt spinning of a plastic material, there has generally been practiced a method whereby the filaments discharged through the spinneret are sent through a spinning tower and taken up in the form of unstretched filaments and the unstretched filaments are subsequently subjected to a stretching treatment for conversion into stretched filaments. Thus, the properties exhibited by the resultant stretched filaments have substantially depended on the properties of the plastic material used as the starting material. Very seldom have these properties been capable of being improved by the spinning process.
U.S. Pat. No. 2,846,289 discloses a method for the manufacture of clear filaments with a surface gloss, which method comprises rapidly cooling polyamide filaments discharged through the spinneret to a temperature below -5.degree.C and subsequently subjecting the filaments to a stretching treatment at normal room temperatures. The filaments manufactured by this method are transparent and have a surface gloss and, therefore, are suitable for specific uses such as in brushes and fishing lines. They, nevertheless, are scarcely improved in terms of tensile strength.
It is a primary object of this invention to provide filaments which are transparent and are possessed of a glossy surface and pronouncedly improved mechanical strengths and a method for the manufacture of such filaments.